Sure, some of America's largest companies contribute millions in products--for example, Microsoft
(nyse:
MSFT -
news
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people
) donated $207 million in products last year. But, when product giving ranges from food to drugs to software, it's difficult to tell who's being the most generous.

To draw up our list of America's most philanthropic companies, we looked at the top Forbes 500s firms by sales and their cash donations for 2002. Data on cash contributions was provided by The Chronicle of Philanthropy.

Calculating total donations, like most accounting, is hardly an exact science. Cash giving can include grants made by a company foundation, contributions made by the company to the foundation and matches of employee gifts.

Most companies budget their donations on the previous year's income. Still, that figure can be marred by unusual items, one-time gains and tax breaks. So, to determine which firms were most generous, we looked at 2002 cash giving as a percentage of 2001 operating income, essentially cash earnings before interest, taxes, depreciation and amortization.